Aromatic tackifier resin

ABSTRACT

The invention comprises a hydrogenated hydrocarbon resin suitable as tackifier for acrylic adhesive polymers, having greater than 20% aromatic protons after hydrogenation, a z-average molecular weight of less than about 1800, a narrow molecular weight distribution, typically of less than or equal to 2.1, and a softening point of from 40° C. to about 120° C. It additionally comprises a method for preparing a hydrogenated aromatic tackifier resin suitable as tackifier for acrylic adhesive polymers comprising the steps of: a) polymerizing under Friedel-Crafts polymerization conditions steam-cracked petroleum distillates, or fractions thereof; having boiling points between about 135° C. and 220° C. and containing at least 40% of by weight vinyl aromatic monomer contents, in the presence of a chain transfer agent; and b) catalytically hydrogenating the results of a) such that at least 75% of the aromaticity is retained. The invention also comprises the use of this hydrogenated hydrocarbon resin as tackifier for an adhesive composition comprising one or more adhesive base polymers selected from acrylic copolymers, styrene block copolymers and ethylene-vinyl ester copolymers wherein improved adhesive properties are observed.

This is a divisional of application Ser. No. 08/333,922, filed Nov. 3,1994, now U.S. Pat. No. 5,656,698 which is a continuation-in-part ofSer. No. 08/148,137 filed Nov. 3, 1993 and is now abandoned.

TECHNICAL FIELD

This invention relates to hydrogenated hydrocarbon resins, methods ofpreparation and uses as tackifiers for adhesive compositions comprisingpolar-group containing copolymers, particularly acrylic copolymers.

BACKGROUND OF THE INVENTION

Acrylic polymer compositions have long been used as adhesivecompositions, particularly in pressure-sensitive adhesive ("PSA")compositions. They exhibit adhesion to a broad variety of surfaces, showgood low temperature performance, generally yield attractively clearadhesives and possess excellent heat, age and UV stability. Acrylicadhesive polymers are available as organic(solvent) solutions, aqueousemulsions and as 100 percent solids, thermoplastic systems that are meltapplied. Perhaps initially most important were the solvent acrylics, butthe environmental/health/safety needs of industry have resulted indramatic growth in water based acrylics.

Traditionally acrylic PSA compositions have been tailored incharacteristics by choice of acrylic monomers and polymerizationconditions. This is unlike many other PSA compositions whichtraditionally have used tackifier resins, diluent oils, antioxidants,etc. to modify and enhance properties. With increasing desirability ofwater based systems and often their demonstration of significantperformance enhancements with tackifier resins, increasing adhesiveperformance demands and a desire to minimize the need to adjust andmodify the acrylics polymerization process, tackifier resins suitablefor acrylics are being sought. Both rosin derivatives, such as rosinesters, and hydrocarbon resins are commercially used as tackifiers insuch blends. The rosin esters have been preferred due to bettercompatibility with acrylics. However, the color and heat, age, and UVstability properties of rosin esters, even when hydrogenated, areinferior to those of acrylics and thus yield compositions of compromisedproperties when used as tackifiers for such systems. Hydrocarbon basedresins have been employed as tackifiers for acrylics, but have oftenlacked the color, stability, compatibility or adhesive performance thatare sought in high performance acrylic adhesive systems, particularlythose based on the more polar acrylic adhesive polymers. Newerhydrocarbon resins suitable as tackifiers for acrylic copolymercompositions are thus being sought, as are acrylic copolymercompositions having improved properties including tack, adhesion, andclarity.

U.S. Pat. No. 5,106,902 addresses internally tackified acrylic copolymercompositions prepared by dissolving a hydrogenated hydrocarbon resin ina liquid monomer mixture from which the copolymer is to be prepared byfree radical initiated emulsion polymerization. A preferred resin is ahydrogenated petroleum resin prepared by Friedel-Crafts polymerizationof steam-cracked petroleum distillates, or fractions thereof, havingboiling points between about 135° C. and 220° C. and containing 10-100%by weight vinyl aromatic monomer contents. Preferably the aromaticcontent of the resin is about 20-65%, most preferably 30-50%. The resinstypically are said to have ring and ball softening points of betweenabout 10° C. and about 100° C.

EP-B-0 196 844 describes the use in aqueous acrylic polymers of anaqueous emulsion of a hydrocarbon resin having a softening point from10° to 120° C. and being a copolymer of predominantly C₅ olefins anddiolefins and from 10 to 60 wt % of one or more monovinyl aromaticcompounds. A preferred range of the monovinyl aromatic compounds is 10to 40 wt %, more preferably 10 to 30 wt %. The resin is not said to behydrogenated and is lacking in compatibility with acrylic polymerscontaining butyl acrylate.

EP-B-0 388 497 describes a hydrocarbon resin tackifier for butylacrylate based polymers wherein the resin is derived from a petroleumcracked distillate comprising unsaturated materials which are C₅ -C₆mono-olefins and monovinyl aromatic monomers. These are used inproportions such that the resin has 35 to 85 wt % aromatic compound,preferably 40 to 70 wt %. The ring & ball softening point is 10° to 90°C., preferably up to 80° C. This resin as well is not said to behydrogenated. In the examples no softening point above 75° C. isillustrated and % aromaticity is not greater than 80%.

SUMMARY OF INVENTION/INVENTION DISCLOSURE

The invention comprises a hydrogenated hydrocarbon resin suitable as atackifier for acrylic adhesive polymers, having greater than 20%aromatic protons by NMR, a z-average molecular weight of less than about1800, a narrow molecular weight distribution, typically of less than orequal to 2.1 polydispersity (M_(w) /M_(n)), and a softening point offrom 40° C. to about 120° C. It additionally comprises a method forpreparing a hydrogenated aromatic tackifier resin suitable as atackifier for acrylic adhesive polymers comprising the steps of: a)polymerizing under Friedel-Crafts polymerization conditionssteam-cracked petroleum distillates, or fractions thereof, havingboiling points between about 135° C. and 220° C. and containing at least40% by weight vinyl aromatic monomer contents, in the presence of 0-40%by weight of polymerization mixture of a chain transfer agent; and b)catalytically hydrogenating the results of a) such that at least 75% ofthe aromaticity is retained. The invention also comprises the use ofthis hydrogenated petroleum resin as a tackifier for an adhesivecomposition comprising one or more adhesive base polymers selected fromacrylic copolymers, styrene block copolymers and ethylene-vinyl estercopolymers wherein improved adhesive properties are observed.

BEST MODE AND EXAMPLES OF THE INVENTION

The hydrogenated petroleum resin of the invention is typically one basedupon catalytic polymerization of principally aromatic monomers whichafter polymerization and hydrogenation retains at least 20% aromaticprotons by NMR, preferably at least 24% aromatic protons. It has az-average molecular weight ("M_(z) ") less than about 1800, preferablyless than 1300, more preferably less than 1100, and most preferably lessthan or equal to 1060. It has a polydispersity (M_(w) /M_(n)), ormolecular weight distribution ("MWD"), of less than 2.1, preferably lessthan 1.90 and a ring and ball softening point (according to ASTM E-28)of 70° to 120° C., preferably 80° to 100° C., more preferably 90° to100° C. The invention resin also preferably exhibits an initial colorafter hydrogenation of greater than or equal to 10 Saybolt, preferablygreater than or equal to 20 Saybolt, most preferably greater than orequal to 24 or 26 Saybolt. The resins meeting this description have beendiscovered to exhibit excellent compatibility with acrylic adhesivepolymers, excellent color characteristics and stability and excellenttackification attributes.

Aromaticity of the invention resins is that measured by ¹ H-NMR, protonNMR, analysis in accordance with generally accepted procedures. The"retained aromaticity" is the ratio of the aromaticity by ¹ H-NMR of thehydrogenated resin to that of the polymerized resin prior tohydrogenation. The molecular weight characterizations are determined bygel permeation chromatography utilizing a polystyrene calibration basisand then converting to a polyisobutylene calibration basis according tothe equation log (MW_(polyisobutylene))=1.11×log(MW_(polystyrene))-0.517. Both procedures are described in relevantliterature, see in particular WO-A-91 07472. The adhesive properties ofadhesive compositions comprising the acrylic polymers and tackifierresins are typically measured in accordance with test methods set by thePressure Sensitive Tape Council ("PSTC").

The terms acrylic polymers, acrylic adhesive polymers and acryliccopolymers are meant to include those polymers made from vinyl acidsand/or esters which are polymerizable under free radical conditions,optionally with other ethylenically unsaturated monomers copolymerizablewith them under the same free radical polymerization conditions.Preferably the vinyl acids and/or esters are selected from the (meth)acrylic acids or alkyl (meth) acrylates. Mixtures of one or more acidsand/or esters are usually included.

These acrylate monomer mixtures generally comprise lower alkyl (meth)acrylates having 1 to 3 carbon atoms in the alkyl group of the ester andupper alkyl (meth) acrylates having 4 or more, usually up to about 14,preferably 4 to 8 carbon atoms. Other monomer components useful inaccordance with the invention are the (meth) acrylic acid(s). Somepreferred examples of monomers are as follows: acrylic acid, methacrylicacid, crotonic acid, maleic acid, itaconic acid, methyl (meth) acrylate,ethyl (meth) acrylate, propyl acrylate, 2-ethylhexyl acrylate, orn-butyl acrylate. Other monomeric material which can be employed caninclude acrylonitrile, vinyl acetate, vinylidene chloride, styrene,methyl styrene, and the like. The monomer mixture would contain from 1%to about 15%, preferably about 2% to about 6% of the (meth) acrylicacid; 0% to about 50%, preferably about 10% to 35%, lower alkyl (meth)acrylate; and from about 25% to 99%, preferably from 60% to about 88%higher alkyl (meth) acrylate. All percents are by weight of the monomermixture.

The resins according to the invention typically can be prepared bycatalytic polymerization of petroleum fractions identified as HeartcutDistillate or HCD and 0-40% by wt. of a chain transfer agent. Table IAillustrates a typical analysis of HCD, however it may vary considerablyas to specific proportions of these typical components.

                  TABLE IA                                                        ______________________________________                                        TYPICAL HEARTCUT DISTILLATE (HCD) COMPOSITION (WT %)                          Component (Wt %)                                                                              Typical Content                                                                           Typical Range                                     ______________________________________                                        toluene         0.10          0-0.2                                           ethyl benzene   0.69        0.01-1.0                                          m/p-xylene      2.68        0.1-5.0                                           styrene         7.83         0.8-10.0                                         o-xylene        3.76        0.1-5.0                                           cumene          0.39        0.01-1.0                                          isopropyl cyclohexane                                                                         1.03        0.4-2.0                                           n-propyl benzene                                                                              2.18        0.8-3.0                                           3-ethyl toluene 3.42        2.5-6.0                                           4-ethyl toluene 1.71        1.0-2.5                                           tri methyl benzene                                                                            1.21        1.0-3.0                                           alpha-methyl styrene                                                                          3.39        2.5-6.0                                           beta-methyl styrene                                                                           0.74        0.5-2.0                                           o/m-methyl styrene                                                                            8.57         5.0-20.0                                         1,2,4-tri methyl benzene                                                                      4.46         3.0-10.0                                         o-methyl styrene                                                                              2.31        1.0-6.0                                           tri methyl benzene                                                                            1.76        1.0-4.0                                           beta-methyl styrene                                                                           1.92        1.0-4.0                                           dicyclopentadiene/cymene                                                                      0.29        0.1-0.8                                           indane          1.31        0.5-2.5                                           indene          9.87         5.0-20.0                                         methyl indane   0.94        0.5-2.0                                           C.sub.4 benzenes                                                                              2.97        2.0-4.0                                           dimethyl styrene                                                                              2.81        2.0-4.0                                           divinyl Benzene 0.99        0.5-2.0                                           C.sub.2 styrenes                                                                              4.71        3.5-5.5                                           methyl indenes  9.69         6.0-11.0                                         naphthalene     2.19        1.0-4.0                                           other non-reactives                                                                           6.08         1.0-10.0                                         ______________________________________                                    

More generally speaking the resins according to the invention can beprepared from vinyl aromatic streams comprising the following.

    ______________________________________                                                                    Table IA                                          Components       Typical Range                                                                            Typical HCD                                       ______________________________________                                        styrene          1-15       8                                                 alkyl derivatives of styrene                                                                   15-40      25                                                indene           5-20       10                                                alkyl derivatives of indene                                                                    3-15       10                                                non-reactive components                                                                        15-76      47                                                ______________________________________                                    

Such streams can be derived from the steam-cracked petroleumdistillates, or fractions thereof, having boiling points between 135° C.and 220° C. so long as they contain or are modified to containsufficient vinyl aromatic contents. For example, an essentially purestyrene component can be added to commercially available petroleumdistillate products that but for styrene otherwise fit this description.In this manner a vinyl aromatic stream comprised of 11.4 wt. % styrene,31.6 wt. % alkyl derivatives of styrene, 17.1 wt. % indene, 5 wt. %alkyl derivatives of indene, and the remainder non-reactive components(34.9 wt. %) was confirmed to be a suitable invention resin feedstock.

Polymerization is generally accomplished in accordance with theteachings of U.S. Pat. No. 4,078,132. According to this teaching,branched chain reactive aliphatic olefins are introduced duringpolymerization as chain transfer agents to achieve both loweredsoftening point and narrowed MWD. Though this document addressespreparation of substantially non-aromatic unsaturated thermoplasticresins, the teaching therein is applicable to feed streams comprisingHCD, or feed streams comprising vinyl aromatic monomer(s), to yield ahighly aromatic precursor resin, which when hydrogenated can yield thearomatic tackifier resin of the invention. The feed streams shouldcontain at least 40% by weight of total polymerizable monomers of vinylaromatic monomers, preferably at least 50% by weight.

The polymerization process of U.S. Pat. No. 4,078,132 is particularlysuitable when practiced at polymerization temperatures of between -20°and 100° C., preferably between 30° and 80° C. in the presence of aFriedel-Crafts catalyst, such as AlCl₃, and in the presence of thebranched chain reactive olefin chain transfer agent, preferablyisoamylenes or dimate. Though most of the branched chain reactive olefincompounds of this prior art document will be effective if used in properamounts, the isoamylenes are more reactive and can be usedadvantageously in lesser amounts. The isoamylenes typically compriseisomers, for example, as shown in Table IB. These reactive chaintransfer agents are preferably used in lesser amount than generallytaught in this document, typically only 10-20, preferably 10-15 wt. %based upon total weight of this HCD or vinyl aromatic feedstream inorder to control softening point and MWD. The process conditions of U.S.Pat. No. 4,514,554 also include description of polymerization ofpetroleum fraction feedstocks including isoamylenes. Both references areincorporated by reference for purposes of U.S. patent practice.

Hydrogenation can be generally accomplished in accordance with theteachings of U.S. Pat. No. 4,629,766, which is also incorporated byreference for purposes of U.S. patent practice. But other conventionalmeans may alternatively be used. Typically temperatures of 200° to 300°C. are used, pressures of 10 to 300 kg/cm², and hydrogenating orhydrotreating catalysts such as Group VIII metals nickel, palladium,cobalt, ruthenium, platinum and rhodium, Group VI metals such astungsten, chromium and molybdenum, and Group VII metals such asmanganese and copper are used. These metals may be used singularly or incombination of two or more metals, in the metallic form, or in anactivated form and may be used directly or on a solid support such asalumina or silica-alumina. A preferred catalyst is one comprisingsulfided nickel-tungsten on a gamma-alumina support having a freshcatalyst surface area ranging from 120-300 m² /g and containing from2-10% by weight nickel and from 10-25% by weight tungsten as describedby U.S. Pat. No. 4,629,766. The hydrogenation is typically carried outwith a hydrogen pressure of 20-300 atmospheres, preferably 150-250atmospheres. Additional description of hydrogenation of aromatic resinsappears in U.S. Pat. No. 3,926,878 and WO-A-91/07472, designated for theU.S. among other countries, both of which are incorporated by referencefor purposes of U.S. patent practice.

Hydrogenation is performed at temperatures, pressures and times, andwith effective catalysts, so as to retain at least 75% aromaticity,preferably at least 80%, more preferably at least 85%, and mostpreferably at least 90%. Optimization of the hydrogenation process canbe empirically accomplished given the teachings presented in thisapplication.

The aromatic tackifier resins of the invention can be used with waterbased acrylics when prepared as resin emulsions in accordance with anyknown means, such as exemplified in U.S. Pat. No. 4,414,346, U.S. Pat.No. 4,486,563 and U.S. Pat. No. 4,487,873. Typically the aromatictackifier resin is emulsified in water and added to the water-basedacrylic polymer to make a pressure sensitive adhesive composition.Alternatively, the tackifier resin can be introduced into the acrylicpolymerization mix for "internal tackification", for example, asdescribed in U.S. Pat. No. 5,106,902, U.S. Pat. No. 5,013,784, U.S. Pat.No. 5,095,065 and U.S. Pat. No. 5,164,441. The disclosures of thesepatents are incorporated by reference for purposes of U.S. patentpractice. The invention resins may also be added directly to solventacrylics or hot melt mixed with thermoplastic acrylics by conventionalmeans.

Typical compositions comprise from 50 to 95 parts by weight acrylicpolymer and 5 to 50 parts aromatic tackifier resin, or preferably 10-30wt. % tackifier resin based upon total of acrylic polymer and resin.

Conventional additive components are often also incorporated in acrylicpolymer compositions and will also be suitable in accordance with thisinvention. Some examples are fillers such as clay, silica and calciumcarbonate and plasticizers such as Paraplex® WP-1, a plasticizer fromRohm and Haas Co. For the water based systems, defoamers, surfactantsand thickeners are commonly used to aid in mixing and coating processes,and biocides are often employed for preservative properties. Seeadditional description in Gehman, D. R., "Acrylic Adhesives", Handbookof Adhesives, 3rd. Ed., pp. 437-450 (Van Nostrand Reinhold, 1990).

Although primarily addressed to adhesive compositions, it will beapparent that the excellent adhesive qualities, color, age and UVstability, and compatibility of the resins in acrylic polymers will alsoprovide advantages when such compositions are used as sealants, anotherarea of significant use for acrylic polymers. Additionally, the resin ofthe invention being high in aromatic content and low in color will beparticularly suitable for use with ethylene-vinyl ester copolymers inhot-melt adhesive compositions, for example as described in U.S. Pat.No. 3,926,878, and with styrene block polymers, for example as describedin WO-A-91 07472. Both references are incorporated by reference forpurposes of U.S. patent practice.

The following examples are presented to illustrate the foregoingdiscussion. All parts, proportions and percentages are by weight unlessotherwise indicated. Although the examples may be directed to certainembodiments of the present invention, they are not to be viewed aslimiting the invention in any specific respect.

EXAMPLE 1

The aromatic resins of this example were polymerized by a continuous,stirred reactor process using aluminum chloride as the catalyst in anitrogen atmosphere at about 10 psig (0.7 kg/cm²). The aluminum chloridecatalyst was added either directly to the reactor in powdered form or inan anhydrous paste form. This was formed by mixing the catalyst with ahydrogenated liquid resin at a weight ratio of 0.6:1. The relativeproportions of catalyst and feedstreams are shown in Table II. Thesewere individually pumped into the continuous stirred tank reactor over aperiod of 6 hours. Water was used as the co-catalyst and was present inthe feedstreams at a level of 50-100 ppm. Thereafter, 200 grams of a 1:3solution of isopropanol and water were added to the final 1200 g.reaction mixture to quench the catalyst. The polymerizate was waterwashed 2 to 3 additional times with the aqueous phase being separatedafter each wash.

The resin recovery step was carried out by heating to 250° C., with anitrogen sparge to remove raffinate followed by steam stripping toproduce the precursor resin.

In this example, an isoamylene stream was used as chain transfer agent,except for Comparative Example D of Table II. The composition of theisoamylene stream for this example and other chain transfer streams aregiven below in Table IB.

                  TABLE IB                                                        ______________________________________                                        TYPICAL CHAIN TRANSFER AGENTS                                                 Component (Wt %)                                                                           Dimate     Amylenes Isoamylenes                                  ______________________________________                                        1-pentene    0.01       20.5     --                                           2-methyl-1-butene                                                                          0.03       30.3     6.55                                         isoprene     --         0.77     --                                           trans-2-pentene                                                                            0.03       17.1     --                                           cis-2-pentene                                                                              0.01       8.45     --                                           2-methyl-2-butene                                                                          0.13       5.36     93.3                                         trans-1,3-pentadiene                                                                       0.02       --       --                                           cis-1,3-pentadiene                                                                         0.01       --       --                                           cyclopentene 0.02       --       --                                           4-methyl-1-pentene                                                                         0.64       --       0.04                                         2,3-dimethyl-1-butene                                                                      1.48       --       --                                           trans-4-methyl-2-pentene                                                                   13.4       --       --                                           2-methyl-1-pentene                                                                         4.10       --       --                                           1-hexene     0.26       --       --                                           trans-3-hexene                                                                             4.02       --       --                                           cis & trans-2-hexene and                                                                   10.2       --       --                                           cis-3-hexene                                                                  2-methyl-2-pentene                                                                         31.3       --       --                                           2,3-dimethyl-2-butene                                                                      2.96       --       --                                           cis-2-hexene 4.27       --       --                                           benzene      0.04       --       --                                           dicyclopentadiene                                                                          --         0.59     --                                           ______________________________________                                    

The following Table II gives the reaction conditions and properties ofthe precursor resins polymerized by the process described above.

                  TABLE II                                                        ______________________________________                                        Resin Example                                                                              A       B       C     D     E                                    ______________________________________                                        Feed Composition, wt. %                                                       Chain Transfer Agent                                                                       14.sup.1                                                                              10.sup.1                                                                              10.sup.1                                                                            0     25.sup.2                             Heartcut Distillate.sup.3                                                                  86      90      90    100   75                                   Polymerization                                                                AlCl.sub.3 Catalyst, wt. %                                                                 0.6     0.6     0.6   0.6   0.6                                  Reactor Temperature, °C.                                                            40      40      40    40    40                                   Reactor Pressure, psig                                                                     10      10      10    10    10                                   (kg/cm.sup.2)                                                                              (0.7)   (0.7)   (0.7) (0.7) (0.7)                                Resin Properties                                                              Softening Point, °C.                                                                92      95      98    112   88                                   .sup.1 H-NMR, % aromatic                                                                   27      nm      29    30    26                                   protons                                                                       Gardner Color                                                                              nm      nm      nm    10    nm                                   GPC Molecular Weight                                                          M.sub.w      450     570     525   860   600                                  M.sub.n      280     290     310   440   330                                  M.sub.w /M.sub.n                                                                           1.6     1.8     1.7   2.0   1.8                                  M.sub.z      760     1010    965   1700  1430                                 ______________________________________                                         notes: 1) Isoamylene; 2) Dimate; 3) HCD is that of Typical Content in         Table IA; 4) "nm" is not measured                                        

The aromatic resins A-E were each blended with 60 wt % of an aliphaticsolvent (Varsol®, Exxon Chemical Co., USA) and then hydrogenated inaccordance with the examples and teachings of U.S. Pat. No. 4,629,766,at a hydrogen pressure of 3800 psig (267 kg/cm²) for 1.5 hours residencetime with an exotherm maximum temperature of 240° C. over the preferredsulfided nickel-tungsten catalyst described above. This resin was thenrecovered by heating to 250° C. with a nitrogen sparge and streamstripping to produce the finished resin.

The thus hydrogenated resins A-E exhibited the characteristics in TableIII. Aged Gardner Color, was as measured after 5 hrs. at a temperatureof 175° C.

                  TABHLE III                                                      ______________________________________                                        Resin Example   A      B       C    D     E                                   ______________________________________                                        Softening Point, °C.                                                                   92     95      98   119   87                                  1H-NMR, % aromatic protons                                                                    24     29      27   29    21                                  Retained Aromaticity %                                                                        89             93   97    81                                  Saybolt color   29     27      28   20    24                                  Aged Gardner Color                                                                            nm     4.0     4.7  17    nm                                  GPC Molecular Weight                                                          M.sub.w         445    520     540  860   530                                 M.sub.n         300    300     330  440   330                                 M.sub.w /M.sub.n                                                                              1.5    1.7     1.6  2.0   1.6                                 M.sub.z         700    920     916  1700  970                                 ______________________________________                                    

EXAMPLE 2

This example illustrates the enhancements available from use of a resinin accordance with the invention when compared against a hydrogenatedrosin ester (Foral® 85 emulsion, Hercules, Inc., U.S.A.) commerciallyused to luckily acrylic adhesive polymers, particularly the more polaracrylic polymers such as those based on butyl acrylate. This inventionresin prepared as in Example 1, after hydrogenation exhibited 25%aromatic protons, an M_(z) of 940, MWD of 1.7, and a ring and ballsoftening point (according to ASTM E-28) of 96° C. The invention resinalso exhibited a color of 14 Saybolt. This resin was then emulsified inaccordance with the teachings of U.S. Pat. No. 4,414,346, U.S. Pat. No.4,486,563, and U.S. Pat. No. 4,487,873. In this case the resinplast usedto facilitate emulsification was heptane.

Robond® PS-83D, Rhoplex® N-619 and Rhoplex® N-580 are water-basedacrylic emulsions available from Rohm & Haas Co. Ucar® 174 is awater-based acrylic emulsion from Union Carbide. These commercialacrylic emulsions are believed to be based on butyl acrylate. Table IVillustrates PSA performance using standard test methods. Each adhesivecomposition was blended in aqueous form in parts by weight (solids ordry basis) and coated onto mylar film to 1.25 mils dry-film thickness.The coated films were dried for 2 min. at 100° C. The films were thencovered with release paper and allowed to set overnight at roomtemperature and 50% humidity.

Both the hydrogenated rosin ester and the invention resin show goodcompatibility with these acrylic polymers as evidenced by the existenceof excellent film clarity. Both resins enhance adhesive aggressivenessand specific adhesion as would be expected of a properly selected resincomposition. However, the invention resin results in much less adhesivesoftening/loss in shear strength ("hold to stainless steel"/creep underload) than the rosin ester. This is a significant drawback associatedwith rosin esters. The invention resin also shows enhancedwetting/adhesion to kraft paper (corrugated board) as demonstrated byfiber tear values. Finally, these attributes are combined with theinvention resin's superior initial color (water white versus 3 Gardnerfor the rosin ester) and color, age and UV stability. Color andstability now more closely match the inherent qualities of acrylicpolymers.

                                      TABLE IV                                    __________________________________________________________________________    Formulations:                                                                              1  2  3  4  5  6  7  8  9  10  11 12                             __________________________________________________________________________    Robond PS-83D                                                                              100         75          75                                       Rhoplex N-619   100         75          75                                    Rhoplex N-580      100         75           75                                Ucar 174              100         75           75                             Invention Resin          25 25 25 25                                          Foral 85                             25 25  25 25                             PSA Performance (1)                                                           Loop Tack to SS, ppi                                                                       1.6                                                                              3.6                                                                              1.2                                                                              3.1                                                                              3.0                                                                              3.1                                                                              2.1                                                                              3.5                                                                              2.6                                                                              4.0 1.7                                                                              4.0                            (g/cm)       (282)                                                                            (635)                                                                            (212)                                                                            (547)                                                                            (530)                                                                            (547)                                                                            (371)                                                                            (618)                                                                            (459)                                                                            (706)                                                                             (300)                                                                            (706)                          Loop Tack to Kraft Paper, ppi                                                              1.9                                                                              2.6                                                                              1.4                                                                              2.2                                                                              1.8                                                                              1.5                                                                              1.8                                                                              1.8                                                                              2.0                                                                              2.3 1.5                                                                              2.0                            (g/cm)       (335)                                                                            (459)                                                                            (247)                                                                            (388)                                                                            (318)                                                                            (265)                                                                            (318)                                                                            (318)                                                                            (353)                                                                            (406)                                                                             (265)                                                                            (353)                          % Fiber Tear (visual)                                                                      2  18 0  1  67 100                                                                              25 67 0  17  5  0                              180° Peel Strength to SS, ppi                                                       2.2                                                                              3.3                                                                              1.5                                                                              3.5                                                                              3.1                                                                              4.1                                                                              2.5                                                                              3.8                                                                              3.4                                                                              6.0 2.3                                                                              4.6                            (g/cm)       (388)                                                                            (582)                                                                            (265)                                                                            (618)                                                                            (547)                                                                            (724)                                                                            (441)                                                                            (671)                                                                            (600)                                                                            (1059)                                                                            (406)                                                                            (812)                          180° Peel Strength to PE, ppi                                                       0.5                                                                              1.3                                                                              0.3                                                                              0.9                                                                              1.3                                                                              0.6                                                                              1.1                                                                              1.7                                                                              1.6                                                                              2.3 1.2                                                                              2.0                            (g/cm)       (88)                                                                             (229)                                                                            (53)                                                                             (158)                                                                            (229)                                                                            (106)                                                                            (194)                                                                            (300)                                                                            (282)                                                                            (406)                                                                             (212)                                                                            (353)                          178° Hold to SS, hrs                                                                11.3                                                                             5.8                                                                              1.8                                                                              4.6                                                                              5.8                                                                              9.3                                                                              11.7                                                                             4.3                                                                              2.8                                                                              3.2 13.0                                                                             2.8                            (0.5" × 0.5" × 500 g)                                             Film Clarity (visual)                                                                      clear                                                                            clear                                                                            clear                                                                            clear                                                                            clear                                                                            clear                                                                            ctear                                                                            clear                                                                            clear                                                                            clear                                                                             clear                                                                            clear                          __________________________________________________________________________     (1) Test methods: loop tack  one inch wide adhesive strip contacted 3-4"      along its length to stainless steel panel and then immediately debonded a     a 2 inches/min jaw separation speed; peel strength  PSTC 1; hold to           stainiess steel (SS)  PSTC 7.                                            

EXAMPLE 3

The performance characteristics of a hydrogenated resin in accordancewith the invention were also compared against commercially availableresins sold as high aromaticity hydrogenated resins. This inventionresin exhibited 24% aromatic protons, an M_(z) of 1050, MWD of 1.6, anda ring and ball softening point (according to ASTM E-28) of 95° C. Theinvention resin also exhibited a color of 26 Saybolt.

Arkon® M-90 and Arkon® P-90 (Arakawa Chemical, Japan) are 90° C.softening point resins indicated by their manufacturer to be aromaticresins hydrogenated to different degrees. Likewise, Arkon® M-100 andArkon® P-100 are 100° C. softening point, aromatic resins with differingdegrees of hydrogenation. Analysis by ¹ H-NMR shows that the inventionresin possesses considerably more aromaticity than the Arkon M series at7.3% and the Arkon P series at 1.2% aromatic protons. Thisdifferentiation yielded much superior performance as an acrylic polymertackifier.

In order to compare resins at equal softening point the Arkon® M-90 andM100 were blended 50/50 to achieve a 95° C. softening point. In the samemanner Arkon® P-90 and Arkon® P-100 were also blended. These blendedcompositions were emulsified in the manner described earlier. Adhesiveperformance comparison with the invention resin is shown in Table V.Adhesive film preparation and test methods are the same as in Example 2.The invention resin clearly exhibits better tack and adhesion than thecommercial hydrogenated aromatic resins (these resins actually reducethe properties of the adhesive base polymers). The invention resin alsoproduces films with greater clarity.

                                      TABLE V                                     __________________________________________________________________________    Formulations:                                                                              1  2  3  4  5  6  7  8  9  10 11 12                              __________________________________________________________________________    Invention Resin                                                                            25 25 25 25                                                      Arkon M-90/100           25 25 25 25                                          Akron P-90/100                       25 25 25 25                              Robond PS-83D                                                                              75          75          75                                       Rhoplex N-619   75          75          75                                    Rhoplex N-580      75          75          75                                 Ucar 174              75          75          75                              PSA Performance (1)                                                           Loop Tack to Kraft Paper, ppi                                                              1.5                                                                              1.4                                                                              1.6                                                                              1.6                                                                              0.2                                                                              0.5                                                                              0.2                                                                              1.1                                                                              0.1                                                                              0  0  0.9                             (g/cm)       (265)                                                                            (247)                                                                            (282)                                                                            (282)                                                                            (35)                                                                             (88)                                                                             (35)                                                                             (194)                                                                            (18)                                                                             (0)                                                                              (0)                                                                              (158)                           % Fiber Tear (visual)                                                                      40 100                                                                              50 90 0  0  0  5  0  0  0  0                               180° Peel Strength to SS, ppi                                                       2.3                                                                              3.4                                                                              2.6                                                                              3.4                                                                              1.0                                                                              1.3                                                                              0.7                                                                              1.2                                                                              0.8                                                                              0.6                                                                              0.5                                                                              1.1                             (g/cm)       (406)                                                                            (600)                                                                            (459)                                                                            (600)                                                                            (177)                                                                            (229)                                                                            (124)                                                                            (212)                                                                            (141)                                                                            (106)                                                                            (88)                                                                             (194)                           180° Peel Strength to PE, ppi                                                       1.1                                                                              0.8                                                                              1.0                                                                              1.5                                                                              0.6                                                                              0.3                                                                              0.4                                                                              0.7                                                                              0.3                                                                              0.2                                                                              0.2                                                                              0.4                             (g/cm)       (194)                                                                            (141)                                                                            (177)                                                                            (265)                                                                            (106)                                                                            (53)                                                                             (71)                                                                             (124)                                                                            (53)                                                                             (35)                                                                             (35)                                                                             (71)                            __________________________________________________________________________     (1) Test methods: loop tack  one inch wide adhesive strip contacted 3-4"      along its length to stainless steel panel and then immediately debonded a     a 2 inches/min jaw separation speed; peel strength  PSTC 1; hold to           stainiess steel (SS)  PSTC 7.                                            

We claim:
 1. A method for preparing a hydrogenated aromatic tackifierresin suitable as a tackifier for acrylic adhesive polymers comprisingthe steps of:a) polymerizing under Friedel-Crafts polymerizationconditions steam-cracked petroleum distillates, or fractions thereof,having boiling points between about 135° C. and 220° C. and containingat least 40% by weight vinyl aromatic monomer contents, in the presenceof 0-40% by weight of polymerization mixture of a chain transfer agent;and b) catalytically hydrogenating the results of the results of a) suchthat at least 75% of the aromaticity is retained.
 2. The methodaccording to claim 1 wherein an isoamylene chain transfer agent is usedin an amount of 10-20% by weight of polymerization mixture.
 3. Themethod according to claim 1 wherein step b) is done using a sulfidednickel-tungsten on a gamma-alumina support.